The studies proposed here compare neural and behavioral responses to a strong natural reward to those seen after drug reward. Salt appetite, provoked by sodium depletion, will be used as a model system for natural motivation and NaCI consumption will be the rewarding event. Studies focus on the mesolimbic dopamine system, which has been shown to be involved in the response to artificial rewards such as drugs of abuse. Because the response of this motivational circuit to natural rewards remains poorly characterized, we will examine patterns of neuronal activation following induction of the drive for sodium and satisfaction of the drive by NaCI ingestion. Neural regions activated by depletion and NaCI intake will be identified by cFos immunostaining. Additionally, we will characterize the necessary conditions for neural activation by a natural motivator and begin to define the neurotransmitter systems involved in the response. Thus, the proposed studies will identify neuroanatomical and neurochemical systems involved in strong natural motivation and define the degree to which these systems overlap with a well-defined system that responds to drugs such as amphetamine.